SEARCH · Search NASA

Results for “Particle acceleration in plasmas”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21

All sources NASA NTRS DOE OSTI

NASA NTRS1981

First-order Fermi acceleration of the diffuse ion population near the earth's bow shock

The flux of 30-65 keV particles observed by the ISEE-3 200 earth radii upstream is shown to be an upstream escape of the energetic ions in the earth's bow shock. A formal solution to the transport equation for the distribution function of energetic particles upstream from an isotropic monoenergetic source of particles/sq cm at a plane shock where the plasma changes speed is found, and escape conditions are defined. The efficiency of the acceleration is calculated to depend on the charge/particle, and fluxes near and far upstream of the shock are described analytically. Any model which takes into account shock acceleration by diffusive scattering with significant escape losses produces the observed spectrum close to the shock. The escape loss upstream is demonstrated to control the spectrum and the variation of flux and anisotropy with distance from the shock.

Forman, M. A.↗

NASA NTRS2017

Impact of Substorm Time O+ Outflow on Ring Current Enhancement

Energetic O+ ions (tens of keV) rapidly increase in the inner magnetosphere and contribute significantly to the ring current during substorms. Previously, two source regions of the energetic O+ ions have been proposed. The first one is the dayside polar region. Ions from the dayside polar region are transported to the lobe; then they are injected to the nightside plasma sheet during substorm expansion phase. The second one is the nightside aurora region. After the substorm onset, energetic O+ ions are extracted from the ionosphere with the auroral acceleration processes, and the O+ ions are directly supplied to the nightside plasma sheet. We investigated the relative importance of these two regions on supplying the energetic O+ ions in the inner magnetosphere. We performed a test particle simulation in global MHD electromagnetic fields. We obtained the following results. (1) During the substorm growth phase, O+ ions at tens of eV are extracted from the dayside polar region, resulting in the enhancement of the warm O+ ions (hundreds of eV) in the lobe. After the substorm onset, the warm O+ ions are nonadiabatically accelerated to tens of keV and injected to the inner magnetosphere. These O+ ions contribute to most of the O+ ring current. (2) O+ ions at less than a few keVs are supplied from the nightside aurora region to the plasma sheet. However, their contribution to the O+ ring current remains small. From the results, we concluded that the main source of the energetic O+ ions is the dayside polar region.

outflow↗

NASA NTRS1977

Observations of energetic electrons /E no less than about 200 keV/ in the earth's magnetotail - Plasma sheet and fireball observations

An earlier paper by the authors (1976) has reported on energetic electron anisotropies observed in conjunction with the acceleration regions identified by Frank et al., (1976). The present paper gives more detailed analyses of observations in the distant plasma sheet, including specific features of intensities, energy spectra, and pitch angle distributions of the very energetic electrons associated with intense plasma particle events, with energies ranging between 50 eV and 45 keV, detected with an electron/isotope spectrometer aboard the earth-orbiting spacecraft Imp 8. Two domains are considered: the plasma sheet and the regions near and within the localized magnetotail acceleration regions known as the fireball regions. The instrumentation used offered a number of observational advantages over many previous studies, including inherently low background, large geometric factors, excellent species identification, good angular distribution measurement capability, and availability of high resolution of differential intensities.

Baker, D. N.↗

NASA NTRS1993

Evidence for ion jets in the high-speed solar wind

Results of an investigation of shapes of proton and alpha particle velocity distribution functions in the high-speed solar wind for the time period from 1973 to 1987 are presented. It is suggested that a modest amount of heating results from the damping of waves, whereas additional heating and the bulk of the acceleration is associated with the direct conversion of magnetic energy flux to plasma convection and enthalpy flux through the process of magnetic reconnection. The present two-component model of heating and acceleration predicts that the ambient flow of plasma from coronal holes is characterized by a low-speed and a low-mass flux. The proton flux is insufficient to drag alpha particles out of the solar gravitational potential well.

Feldman, W. C.↗

NASA NTRS1994

Comprehensive Plasma Instrumentation (CPU) for the Geotail spacecraft

Geotail was launched on 24 July 1992 as the first new spacecraft of the International Solar Terrestrial Physics Program (ISTP). A primary objective of the Geotail mission is the acquisition of particles and fields measurements in the tail region of the magnetosphere. Some of the specific scientific objectives of the Geotail mission are; (1) assessment of the relative importance of solar-wind and ionospheric sources to the plasmas of the magnetotail, (2) a search for plasmoids and flux ropes, (3) direct observation of the effects of plasma acceleration and heating in the current sheet, and (4) measurements of currents and convective flows carried by magnetotail plasmas. The Comprehensive Plasma Instrumentation (CPI) aboard the Geotail spacecraft provides observations of the charged particles that comprise the plasma populations of the magnetosphere and the solar wind. In many cases the physical processes that contribute to the flow of energy and mass through the Solar-Terrestrial plasma system can be understood only through a detailed examination and analysis of the distribution of the particle velocities in the ambient plasmas. The CPI provides detailed measurements of these distributions. It employs three plasma analyzers: (1) the Hot Plasma analyzer (CPI-HP) for hot electrons and ions found in the plasma sheet and the inner magnetosphere; (2) a Solar Wind analyzer (CPI-SW) for cool plasmas with high bulk speeds such as those found in the solar wind and magnetosheath; and (3) an Ion Composition analyzer (CPI-IC) for identification of ion species such as H(+), He(+), He(++), and O(+). Along with measurements from other fields and particles instrumentation on Geotail, the CPI measurements provide a fundamental experimental base for investigations of solar-terrestrial plasmas and fields.

Frank, Louis A.↗

NASA NTRS1998

Central Plasma Sheet Ion Properties as Inferred from Ionospheric Observations

A method of inferring central plasma sheet (CPS) temperature, density, and pressure from ionospheric observations is developed. The advantage of this method over in situ measurements is that the CPS can be studied in its entirely, rather than only in fragments. As a result, for the first time, comprehensive two-dimensional equatorial maps of CPS pressure, density, and temperature within the isotropic plasma sheet are produced. These particle properties are calculated from data taken by the Special Sensor for Precipitating Particles, version 4 (SSJ4) particle instruments onboard DMSP F8, F9, F10, and F11 satellites during the entire year of 1992. Ion spectra occurring in conjunction with electron acceleration events are specifically excluded. Because of the variability of magnetotail stretching, the mapping to the plasma sheet is done using a modified Tsyganenko [1989] magnetic field model (T89) adjusted to agree with the actual magnetotail stretch at observation time. The latter is inferred with a high degree of accuracy (correlation coefficient -0.9) from the latitude of the DMSP b2i boundary (equivalent to the ion isotropy boundary). The results show that temperature, pressure, and density all exhibit dawn-dusk asymmetries unresolved with previous measurements. The ion temperature peaks near the midnight meridian. This peak, which has been associated with bursty bulk flow events, widens in the Y direction with increased activity. The temperature is higher at dusk than at dawn, and this asymmetry increases with decreasing distance from the Earth. In contrast, the density is higher at dawn than at dusk, and there appears to be a density enhancement in the low-latitude boundary layer regions which increases with decreasing magnetic activity. In the near-Earth regions, the pressure is higher at dusk than at dawn, but this asymmetry weakens with increasing distance from the Earth and may even reverse so that at distances X less than approx. 10 to -12 R(sub E), depending on magnetic activity, the dawn sector has slightly higher pressure. The temperature and density asymmetries in the near-Earth region are consistent with the ion westward gradient/curvature drift as the ions ExB convect earthward. When the solar wind dynamic pressure increases, CPS density and pressure appear to increase, but the temperature remains relatively constant. Comparison with previously published work indicates good agreement between the inferred pressure, temperature, and density and those obtained from in situ data. This new method should provide a continuous mechanism to monitor the pressure, temperature, and density in the magnetotail with unprecedented comprehensiveness.

Wing, Simon↗

NASA NTRS1979

Pitch angle distributions of energetic protons near the earth's bow shock

Measurements of energetic protons between about 28 and about 145 keV on ISEE-1 upstream and downstream of the earth's bow shock during times of a radial interplanetary magnetic field are presented. The protons exhibited a slight antisunward flow in the spacecraft system in front of the bow shock and a strong flow along the magnetic field in the spacecraft system in the magnetosheath. Compton-Getting transformations of these anisotropies into the plasma frame of reference have been performed. It is argued that the observations can be explained best in terms of particle acceleration by multiple reflection between the bow shock and upstream scattering centers.

Scholer, M.↗

NASA NTRS1979

Jupiter's magnetosphere and radiation belts

Radioastronomy and Pioneer data reveal the Jovian magnetosphere as a rotating magnetized source of relativistic particles and radio emission, comparable to astrophysical cosmic ray and radio sources, such as pulsars. According to Pioneer data, the magnetic field in the outer magnetosphere is radially extended into a highly time variable disk-shaped configuration which differs fundamentally from the earth's magnetosphere. The outer disk region, and the energetic particles confined in it, are modulated by Jupiter's 10 hr rotation period. The entire outer magnetosphere appears to change drastically on time scales of a few days to a week. In addition to its known modulation of the Jovian decametric radio bursts, Io was found to absorb some radiation belt particles and to accelerate others, and most importantly, to be a source of neutral atoms, and by inference, a heavy ion plasma which may significantly affect the hydrodynamic flow in the magnetosphere. Another important Pioneer finding is that the Jovian outer magnetosphere generates, or permits to escape, fluxes of relativistic electrons of such intensities that Jupiter may be regarded as the dominant source of 1 to 30 MeV cosmic ray electrons in the heliosphere.

Kennel, C. F.↗

NASA NTRS1987

A boundary layer model for magnetospheric substorms

An alternative framework for understanding magnetospheric substorm activity is presented. It is argued that observations of magnetic field and plasma flow variations in the magnetotail can be explained in terms of the passage of the plasma sheet boundary layer over the satellite detecting the tail signatures. It is shown that field-aligned currents and particle acceleration processes on magnetic field lines threading the ionospheric Harang discontinuity lead to the distinctive particle and field signatures observed in the magnetotail during substorms. It is demonstrated that edge effects of field-aligned currents associated with the westward traveling surge can lead to the negative B(z) perturbations observed in the tail that are presently attributed to observations made on the anti-earthward side of a near-earth neutral line. Finally, it is shown that the model can provide a physical explanation of both the driven system and the loading-unloading system whose combined effects provide the observed substorm perturbation pattern in the magnetosphere and ionosphere.

Rostoker, Gordon↗

NASA NTRS1988

Particle acceleration in accreting magnetospheres

The possibility that energetic protons are accelerated within the closed magnetosphere of accelerating neutron stars is considered. The accelerating mechanism is suggested to be plasma turbulence excited by the accretion flow. Rough estimates show that this mechanism may be capable of accelerating protons to the energies of about 10 to the 16th eV required to explain observations of about 10 to the 15th eV gamma rays from some thermal X-ray sources. Proton synchrotron radiation may be observable at energies ranging from the infrared to about GeV gamma rays.

Katz, J. I.↗

NASA NTRS1990

Particle injection and acceleration at earth's bow shock - Comparison of upstream and downstream events

The injection and acceleration of thermal solar wind ions at the quasi-parallel earth's bow shock during radial interplanetary magnetic field conditions is investigated. Active Magnetospheric Particle Tracer Explorers/Ion Release Module satellite observations of complete proton spectra, and of heavy ion spectra above 10 keV/Q, made on September 12, 1984 near the nose of the shock, are presented and compared to the predictions of a Monte Carlo shock simulation which includes diffusive shock acceleration. It is found that the spectral observations are in good agreement with the predictions of the simulation when it is assumed that all accelerated ions originate in the solar wind and are injected into the acceleration mechanism by thermal leakage from the downstream plasma. The efficiency, which is determined directly from the downstream observations, is high, with at least 15 percent of the solar wind energy flux going into accelerated particles. The comparisons allow constraints to be placed on the rigidity dependence of the scattering mean free path and suggest that the upstream solar wind must be slowed substantially by backstreaming accelerated ions prior to undergoing a sharp transition in the viscous subshock.

Ellison, Donald C.↗

NASA NTRS1986

On a difficulty with accelerating particles at slow-mode shocks

The available information on slow-mode shocks is briefly reviewed in order to determine whether these shocks are capable of accelerating particles to high energies, thus providing a possible mechanism for energetic particle production at reconnection sites. It is noted that in contrast to fast shocks, the evolutionary conditions at a steady slow shock require the upstream plasma to flow into the shock with a normal component slower than the intermediate speed. Consequently, the right-polarized waves will escape from a slow shock, and backstreaming particles scattered by these waves will not be convected back to the shock. There will be no effective compression, and further acceleration will not occur.

Isenberg, P. A.↗

NASA NTRS1978

Probing the solar corona with energetic particles

Representative sets of recent experimental results and theoretical studies are summarized to show the current knowledge of energetic particle phenomena based mainly on observations near 1 AU. Measurements close to the sun of quantities such as particle spectra, charge and isotopic composition, and the flow of particles as a function of time, together with measurements of the plasma, magnetic field, X-rays, and gamma rays will not only reveal the properties of the source region and acceleration mechanisms but will also provide a better knowledge of the physics of the corona. These measurements may also reveal the existence of large scale inhomogeneities in the solar corona. The general requirements for making these measurements on the solar probe are listed. An energetic particle detector system which has the capability of resolving the charge and isotopic composition up to 50 MeV/nucleon may successfully measure the above quantities provided that it can perform under both very low and average intensity levels.

Vanhollebeke, M. A. I.↗

NASA NTRS1986

MAX '91: An advanced payload for the exploration of high energy processes on the active sun

The results of a NASA science working group established to study a follow-on to the Solar Maximum Mission are given. A complement of instruments is suggested, with the primary objective of studying the physics of energetic processes in cosmic plasmas by observing high-energy phenomena in solar flares. High-quality flare observations will be possible with these instruments during the next peak in solar activity expected to last from 1990 through at least 1995. The primary objective of MAX '91 is to study energetic processes in cosmic plasmas by observing high-energy phenomena in solar flares. These processes, which are of general astrophysical importance, include energy release, particle acceleration, and energy transport. Results from comprehensive observing programs conducted during the last solar cycle have demonstrated the great scientific potential of high-energy emissions for addressing these central physical processes. Consequently, a payload optimized for observations of high-energy solar flare phenomena is suggested for MAX '91. It consists of the following four specific instruments: (1) a Fourier-transform X-ray and gamma-ray imager covering the energy range from a few keV to 1 MeV with arcsecond spatial resolution; (2) a cooled germanium X-ray and gamma-ray spectrometer with keV spectral resolution covering the energy range from 10 keV to 50 MeV; (3) Bragg spectrometers with high spectral resolution at wavelengths between 1 and 9 angstrons; and (4) a soft X-ray, EUV, or UV imaging instrument with arcsecond spatial resolution.

Source record↗

NASA NTRS1993

Dynamics explorer data analysis

Work in the following areas is discussed: plasma physics of the auroral acceleration region; electrodynamic coupling as a function of substorm phase and interplanetary magnetic field (IMF) direction; and particle injection in the magnetospheric cusp.

Reiff, Patricia H.↗

NASA NTRS1998

Determination of Particle Sources for a Geotail Distribution Function Observed on May 23, 1995

On May 23, 1995, the Comprehensive Plasma Instrumentation (CPI) onboard the Geotail spacecraft observed a complex and structured ion distribution function near the magnetotail midplane at x approximately -10 R(sub E). On the same day, the Wind spacecraft observed a very high density (approximately 40/cubic cm) solar wind and an interplanetary magnetic field (IMF) that was predominantly northward but had several southward turnings. We have inferred the sources of the ions in this distribution function by following approximately 90,000 ion trajectories backward in time using time-dependent electric and magnetic fields obtained from a global MHD (magnetohydrodynamic) simulation. Wind data were used as input for the MHD model. We found that three sources contributed to this distribution: the ionosphere, the plasma mantle which had near-Earth and distant tail components, and the low latitude boundary layer (LLBL). Moreover, distinct structures in the low energy part of the distribution function were found to be associated with individual sources. Structures near 0 deg pitch angle were made up of either ionospheric or plasma mantle ions, while structures near 90 deg pitch angle were dominated by ions from the LLBL source. Particles that underwent nonadiabatic acceleration were numerous in the higher energy part of the ion distribution function, whereas ionospheric and LLBL ions were mostly adiabatic. A large proportion of the near-Earth mantle ions underwent adiabatic acceleration, while most of the distant mantle ions experienced nonadiabatic acceleration.

Ashour-Abdalla, M.↗

NASA NTRS2004

Complexity and Intermittent Turbulence in Space Plasmas

Sporadic and localized interactions of coherent structures arising from plasma resonances can be the origin of "complexity" of the coexistence of non- propagating spatiotemporal fluctuations and propagating modes in space plasmas. Numerical simulation results are presented to demonstrate the intermittent character of the non-propagating fluctuations. The technique of the dynamic renormalization-group is introduced and applied to the study of scale invariance of such type of multiscale fluctuations. We also demonstrate that the particle interactions with the intermittent turbulence can lead to the efficient energization of the plasma populations. An example related to the ion acceleration processes in the auroral zone is provided.

Chang, Tom↗

NASA NTRSDate not supplied

Filling the Gaps in Understanding Solar Flares

Solar flares provide a laboratory for plasma physics and magnetohydrodynamic processes. While the mechanism of transferring magnetic flux between topological domains via reconnection is accepted in a general sense, some of the finer details remain to be worked out: What elusive thresholds, pertaining to which physical quantities, determine the initiation of flux transfer that cascades into the energy release observed in the impulsive phase of a flare? What role does turbulence play in accelerating or prolonging magnetic reconnection? To what degree do magnetic waves contribute to the transport of energy, or to the acceleration of particles in the impulsive phase? While our innate human curiosity and our instinctive impulse to explore compel us to investigate these intricacies of million-degree magnetized plasmas, the impacts of space weather on our technology-dependent society and economy obligate us to pursue a quantitative understanding, with the ultimate goal being trustworthy predictive capabilities. In this presentation, I will touch upon a few aspects of solar flares where improvements in observational and analytical capabilities can be expected to help us fill gaps in our understanding, as well as some of the recent, current, and near-term developments that are carrying the field forward.

David E. McKenzie↗